GB2381326A

GB2381326A - Mounting an optical fibre to an optical chip

Info

Publication number: GB2381326A
Application number: GB0125763A
Authority: GB
Inventors: Christopher James Hurr; Richard Webb; Ebrahim Irvani
Original assignee: Bookham Technology PLC
Current assignee: Lumentum Technology UK Ltd
Priority date: 2001-10-26
Filing date: 2001-10-26
Publication date: 2003-04-30
Also published as: GB0125763D0

Abstract

A retainer 15 or 115 for mounting an optical fibre 11 in a mounting channel 13 of an optical clip 20 has a mounting portion 17 or 117 and a clamping portion 31 or 121, there being a chamfer surface 19 or 119 for guiding the optical fibre into the channel 13. The retainer may be formed of spring steel or in the form of a sintered ceramic block (or like material). The retainer may be used with a guide block having a groove 47 thereon, an open upper end of which terminates in chamfered guide surfaces 49. A method of guiding the fibre 11 into the channel 13 is also disclosed, together with a kit and an assembly of the kit with the chip and optical fibre.

Description

IMPROVEMENTS IN MOUNTING AN OPTICAL FIBRE TO AN OPTICAL CHIP Field of the Invention The present invention relates to improvements in mounting an optical component to a substrate. In particular, the present invention relates to improvements in guiding an optical fibre into position for mounting to an optical chip.

Background of the Invention An optical chip may have one or more circuit elements which, for example, either produce photocurrent, emit light in response to an injection of electric current or multiplex or demultiplex light signals of different wavelengths. In some applications, the optical chip may be housed in a"package"having pins for connecting at least some of the circuit elements to a printed circuit board. Such packages are described in, for example, International patent application publication WO 00/02079 (Bookham Technology Limited/Yeandle et al.) and US patent No. 6,078, 711 (Bookham Technology PlclYeandle et al.). These packages provide electrical and environmental shielding for the optical chip. Typically, one or more optical fibres extend into the package and are mounted on the optical chip to transmit light to, or from, the circuit element (s).

The optical chip usually has a silicon substrate on a surface of which one or more circuit elements are formed together with one or more optical waveguides for coupling a circuit element to an optical fibre. The silicon substrate is usually mounted on an insulator inside the package.

Correct alignment of the optical fibre with respect to the optical chip is necessary in order that there is optimal optical coupling between the optical chip and the optical fibre. One method of attaching an optical fibre to an optical chip is by mounting the optical fibre in a channel provided in the surface of the substrate of the optical chip, for example by etching. Typically, such channels extend from

an edge of the substrate surface to a waveguide. When etched, the shape of the channel is determined by the way that etching occurs along specific crystallographic planes of the substrate material. Consequently, a channel chemically etched in a silicon substrate has a V-shaped cross section and an end face that slopes away from the edge. The V-shaped channel may have a flat- bottomed surface depending on the depth of the etch.

Usually, the optical fibre is attached to the channel with adhesive or solder.

Attachment of the optical fibre in this way provides the optical fibre with resistance to axial withdrawal forces, that is, forces along the axis of the fibre. However, the optical fibre is not securely held against forces tending to peel the fibre out of the channel.

In order to overcome this problem, a mechanical constraint or retainer may be additionally used to secure the optical fibre in the channel. For example, US patent No. 6,078, 711 proposes the use of a retainer that is attached with adhesive to the edge of the substrate surface at the entrance to the channel. In one embodiment, the retainer has an aperture through which the optical fibre projects into the channel. In another embodiment, the retainer, when fixed to the edge, has an inverted U-shape so that the edge of the substrate and the inner surface of the legs and the base of the retainer define an aperture through which the optical fibre projects into the channel. Although these retainers tend to resist peeling movement of the optical fibre, the optical fibre tends not to lie flat and straight in the V-shaped channel unless the retainer is used correctly, which is difficult. In particular, the positioning of the retainer is operator dependent and tends to be a time-consuming procedure. If the retainer is not attached accurately then the optical fibre may be damaged or deformed. Furthermore, the retainer may pick up dirt when examined to ensure that it is placed on the fibre in the correct orientation and the retainer may not sit squarely against the substrate. Moreover, it is vital that the correct amount of adhesive is used.

United Kingdom patent application GB 0108747.7 (Bookham Technology Plc.) discloses an improved way of mounting an optical fibre to an optical chip by

using a clamping block having a V-shaped groove in its underside which is mounted on the substrate of the optical chip to hold the fibre in place. This arrangement secures the fibre against forces tending to peel the fibre out of the channel.

Although such mechanical restraints prevent the optical fibre from being peeled out of the mounting channel, they require that the optical fibre be located in, or in the close vicinity to, the mounting channel prior to attachment of the restraint to the substrate. Consequently, the mounting of the optical fibre can be time-consuming and the optimal alignment of the fibre in the channel is difficult to achieve.

It is an aim of the present invention to provide improvements to the way in which an optical component, in particular an optical fibre, is mounted to an optical chip. In particular, it is an aim of the present invention to provide a way of guiding an optical component into the mounting channel on an optical chip. Furthermore, it is an aim of the present invention to provide a way of guiding an optical component into a retaining means already mounted in position on the optical chip for retaining the optical fibre in the mounting channel.

Summary of the Invention According to the present invention, there is provided a retainer for retaining an optical component having a generally curvilinear cross section in a mounting channel which extends along the surface of a substrate from a first edge of the substrate, the retainer having a mounting portion and a clamping portion, and including a chamfer surface such that, in use, with the mounting portion attached to the substrate or a support therefor and where the optical component is moved towards the retainer from the first edge of the substrate, the chamfer surface acts to deflect the optical component into the mounting channel and into a position where the optical component is retained in the mounting channel by the clamping portion.

Preferably, the chamfer surface deflects the optical component downwardly into the mounting channel. Alternatively, the chamfer surface deflects the optical component towards the mounting channel across the surface of the substrate. In a preferred embodiment, the retainer comprises more than one chamfer surface.

The chamfer surface may be on any part of the retainer. Preferably, the clamping portion of the retainer comprises a chamfer surface terminating in a clamping edge or edge region.

In a preferred embodiment, the clamping portion comprises a resilient portion which is biased such that the resilient portion adopts a first position relative to the mounting portion and wherein, in use, interaction between the resilient portion and the optical component prevents the resilient portion adopting said first position and the resilient portion applies a clamping force on the optical component substantially in the direction of the mounting channel.

Thus, a retainer comprising a resilient portion is able to retain an optical component in the mounting channel of a substrate by using the resilient portion to bias the optical component downwardly into the substrate on which it is mounted.

In this way, the retainer may secure the optical component against both axial and transverse displacement without the need for an adhesive. Therefore, an optical component secured to an optical chip using this embodiment of the retainer of the present invention will lie flat along the channel in the substrate of the optical chip, providing optimum and readily reproducible alignment of the optical component and optical chip.

The resilient portion may be any suitable shape. Preferably, the resilient portion provides tangential contact with the optical component having a generally curvilinear cross section. Tangential contact between the resilient portion and the optical component may be provided by virtue of the curvilinear cross section of the optical component and/or by at least an edge portion of the resilient portion having a curvilinear shape, i. e. the edge portion is convexly curved. By having tangential

contact between the resilient portion and the optical component, there is likely to be less deformation of or damage to the optical component.

The retainer may be used to fix an optical component permanently or temporarily in the mounting channel of a substrate. Preferably, the retainer is intended to be used as a permanent fixing device.

Where the clamping portion comprises a resilient portion, the retainer is preferably made of a material that enables the resilient portion to retain its resilient properties over the expected operating temperature range of the optical package in which the retainer is to be incorporated. Preferably, the resilient portion of the retainer retains its resilient properties over the temperature range-40 C to +85 C.

Preferably, the retainer is made from spring steel, phosphorous bronze, Be-Cu alloy or a plastic material. More preferably, the whole of the retainer is made from a resilient material, such as spring steel.

Preferably, the optical component retained by the retainer is an elongate element. More preferably, the optical component is an optical fibre. By "optical fibre"is meant any part of an optical cable that has been stripped of any protective buffer layer, polymer layers or sheath to leave only the central optical core surrounded by the optical cladding layer. Light transmitted down the optical fibre travels through the central optical core and is retained therein by total internal reflection at the interface with the optical cladding.

The mounting portion of the retainer may be of any form and, in use, may be adhered to any surface in the package within which the substrate is to be mounted. By"package"is meant herein a package like that in which an optical chip is housed as disclosed in WO 00/02079. Preferably, the mounting portion of the retainer is attached to the substrate, for example an optical chip. Alternatively, where the substrate is located on a further substrate, for example, where the optical chip is mounted on an insulating material, the mounting portion may be attached to the further substrate. The mounting portion of the retainer may be attached in any suitable manner, for example, using an adhesive or by soldering,

welding (e. g. laser welding), clipping, pinning, riveting or, if it is to be attached to a plastics surface of the package, by heat staking.

The mounting portion of the retainer may comprise feet and a recessed portion such that, when the retainer is placed on the substrate, the undersides of the feet of the mounting portion touch the substrate leaving a gap between the recessed portion of the mounting portion and the substrate. Adhesive or solder is applied in this gap and not to the underside of the feet of the mounting portion. In this way, the height of the retainer above the substrate, and hence the mounting channel, can be carefully regulated as any fluctuations in the thickness of the adhesive or solder layer do not affect the position of the feet of the mounting portion above the substrate.

In an alternative embodiment of the invention, the retainer is in the form of a solid block, which may be formed in a moulding operation, the block having a mounting portion and a guiding portion, wherein the guiding portion comprises a chamfer surface such that, in use, with the mounting portion attached to the substrate or support therefor and where the optical component is moved towards the mounting channel, the chamfer surface acts to deflect the optical component into the mounting channel, the guiding portion terminating in a clamping edge or edge region providing said clamping portion.

The retainer may be made of any suitable material or combination of materials, such as machined ceramic.

Preferably, the chamfer surface deflects the optical component in a direction normal to the longitudinal axis of the mounting channel in the plane of the surface of the substrate.

Preferably, the chamfer surface is oriented such that it deflects the optical component so that the optical component is moved downwardly towards the mounting channel. Further chamfer surfaces may be provided on the block which

are oriented such that they deflect the optical component towards the mounting channel across the surface of the substrate.

It is preferred that the retainers described above are each used with a guide block for initially guiding the optical component into the mounting channel, the guide block having a mounting portion and a guiding portion, wherein the guiding portion comprises an upwardly open groove terminating at its upper end in two opposed chamfer surfaces, whereby, in use, with the guide block attached, or adjacent, to the first edge of the substrate with the groove in line with the mounting channel, when the optical component is moved towards the mounting channel, the groove can be used to guide the optical component into line with, and into, the mounting channel.

In a further aspect of this invention there is provided a kit comprising a retainer as described above and a guide block as described above In another aspect of this invention there is provided an assembly comprising a substrate having a surface in which is formed a mounting channel which extends from a first edge of the substrate, an optical component having a generally curvilinear cross section disposed in the mounting channel, a retainer and preferably also a guide block, the retainer having a mounting portion and a clamping portion wherein the mounting portion of the retainer is attached to the substrate or a support therefor such that the clamping portion contacts the optical component to clamp it in the mounting channel, the guide block having a mounting portion and a guiding portion wherein the mounting portion is attached, or adjacent, to the first edge of the substrate, and wherein the retainer and the guide block both include a chamfer surface thereon for guiding the optical component into the mounting channel.

The mounting channel may be of any suitable cross section such as tapered, e. g. V-shaped or curvilinear. Preferably, the cross section of the mounting channel is V-shaped. Furthermore, the mounting channel may have

dimensions suitable for placing a single optical component or more than one optical component therein.

The optical component may be an optical fibre and the substrate a part of an optical chip. Alternatively, the optical component may be a ball lens and the substrate a part of an optical chip.

Where there is more than one optical component in the mounting channel, the optical components may lie side by side or one in front of the other in the channel. Preferably, where more than one optical fibre is present in the mounting channel, the optical fibres lie in the mounting channel with their longitudinal axes in parallel. Where both a ball lens and an optical fibre are present in an assembly according to the present invention, the ball lens is preferably located at the end of the mounting channel between the optical chip and the optical fibre. Where the assembly comprises a mounting channel with more than one component, the retainer may have a resilient arm or clamping portion which contacts both components. Alternatively, more than one retainer may be used in the assembly of the present invention.

Preferably, there is a further portion of the optical component projecting from the mounting channel. In particular, where the optical component is an optical fibre, the optical fibre may project from the mounting channel and, for example, extend into the entry portion of a package holding the assembly.

According to another aspect of the present invention, there is further provided a method of guiding an optical component having a generally curvilinear cross section into a mounting channel which extends along the surface of a substrate from a first edge of the substrate comprising the steps of: preferably attaching at, or adjacent to, the first edge of the substrate a guide block having a mounting portion and a guiding portion wherein the guiding portion comprises a chamfer surface; placing over the mounting channel a retainer having a mounting portion, a clamping portion and a chamfer surface; bringing the optical component in contact with the chamfer surface on the guiding portion of the guide block and

then in contact with the chamfer surface on the retainer to deflect the optical component into the mounting channel such that the optical component at least partially lies between the mounting channel and the clamping portion of the retainer.

By way of example, embodiments of the present invention will now be described with reference to the accompanying Figures of drawings.

Brief Description of the Figures of Drawings FIGURE 1 is a schematic perspective view of a base of a package housing an optical chip and with which a retainer according to the present invention is able to be used to guide and clamp an optical fibre in the mounting channel shown therein; FIGURE 2 is an enlarged perspective view of a first embodiment of retainer on the optical chip in the package, together with a guide block, which is optional; and FIGURE 3 is a view similar to FIGURE 2, but showing a second embodiment of retainer.

Detailed Description of the Exemplary Embodiments In the following description, like reference numerals are used to identify like features in the different embodiments.

Referring to the drawings, there is shown in FIGURE 1 a base 1 of a package for an integrated optical chip 20 having a silicon substrate 23 on which is formed one or more opto-electronic circuit elements and one or more associated waveguides (not shown), as known in the art. The base 1 has a recess 3, to the floor of which the optical chip 20 is coupled through a ceramic insulator 21, and includes electrically conducting pins 5 to electrically connect one or more of the

opto-electronic circuit elements to a printed circuit board. The base 1 also has a tubular extension 7 to which an optical cable 9 is coupled. Although not shown, the package further includes a lid to cover the recess 3. The package acts to provide electrical shielding and hermetic sealing for the optical chip 20. The package may be formed from Kosar, an alloy of nickel, cobalt and iron.

There is a mounting channel 13 that has been chemically etched in the silicon substrate, for example using the procedure outlined in US Patent No.

5,787, 214 (Bookham Technology Ltd./Harpin et a/), the entire contents of which are hereby incorporated herein by reference. The mounting channel 13 extends from the edge 27 of the silicon substrate 23 along a part of the upper surface 29 of the silicon substrate 23 and, as can be seen in FIGURES 2 and 3, has walls 33 providing a V-shaped cross section. The mounting channel 13 may have a depth of about 50 to 100 um, preferably about 80 to 100 pm. The width of mounting channel 13 at the upper surface 29 of the substrate 23 may be about 140 to 150

, um, preferably about 143 to 146 um.

The optical cable 9 is secured, in use, to the inner surface of the tubular extension 7. Preferably a ferrule as described in WO 00/02079, the entire contents of which are hereby incorporated herein by reference, is used to secure the optical cable 9 within the tubular extension 7.

In FIGURE 1, the optical cable 9 is shown in its desired location in the channel 13.

As detailed in WOOO/02079 supra, at the end of the optical cable 9 nearest the package 1, the outer sheath has been stripped to provide an optical fibre 11. The optical fibre 11 has a diameter in the range about 100 to 150 pm, preferably

about 125 um, with the core having a diameter in the range of about 5 to 10 um. The optical fibre 11 is arranged to lie in and be aligned with the mounting channel 13. Prior to insertion into the package, the optical fibre 11 may be cleaved using any suitable cleaving apparatus. The particular type of cleaving apparatus used is not important, as will be understood by the skilled person in the art. One type of

mechanical cleaver is the FK12 angled fibre cleaver (York Technologies Limited) while laser cleavers are available from Optek or AEA Technology.

Referring now specifically to FIGURE 2, a retainer 15 of a resilient material, such as spring steel, has a mounting portion, comprising two legs 17, and a clamping portion 19. The two legs 17 are attached to the upper surface 9 of the substrate 23 by a layer of adhesive between the mounting portion 17 and the upper surface 29, or in any other suitable manner. The clamping portion 19 is generally rectangular, and terminates in a convexly curved edge region 31. In use, the retainer 15 is positioned over the optical fibre 11 (not shown in FIGURE 2) and mounting channel 13 such that the clamping portion 19, or at least the edge region 31, extends generally at right angles to the longitudinal axis of the channel 13. The clamping portion 19 is resilient and, prior to the insertion of the optical fibre 11 into the channel 13, the curved edge region 31 of the retainer 15 adopts a first position in engagement with the upper surface 29 of the substrate 23.

Optionally, a guide block 41 is used with the retainer 15, the guide block 41 having a base providing a mounting portion 43 and a guiding portion 45 comprising an upwardly opening groove 47 terminating in two outwardly inclined chamfer surfaces 49.

In use, the mounting portion 43 of the guide block 41 is mounted to the ceramic insulator 21 so that the guide block 41 is attached to the first edge 27 of the substrate (or located adjacent thereto), as shown in FIGURE 2, and the retainer 15 is located inwardly thereof, and attached to the upper surface 29 of the substrate 23, or to a support therefor. When so located, it is a relatively simple task to locate the optical fibre 11 in the mounting channel 13, and retain it in position therein.

The retainer 15 is placed in position over the mounting channel 13 and, optionally, the guide block 45 is placed in position against, or adjacent, the edge 27 before the optical fibre 11 is located in the mounting channel 13. Any suitable method of positioning the retainer 15 and block 41 may be used, for example,

using a pick-and-place machine. Pick-and-place machines are well known to those skilled in the art and are widely used in the field of electronics. One such machine is the Micron 2 available from ESEC (ZEVATECH). Typically, the pick- and-place machine has a vacuum tool to hold and move the retainer 15 and a load sensor that stops further movement of the retainer 15 when the legs 17 of the retainer 15 contact the upper surface 29 of the substrate 23 or an adhesive layer thereon. In an alternative embodiment (not shown), the legs 17 are attached to the ceramic insulator 21 and the pick-and-place machine has a load sensor that stops further movement of the retainer 15 when the mounting portion 17 contacts the ceramic insulator 21 or the adhesive layer thereon. The guide block 41 can be placed in position in a somewhat similar manner.

To locate the optical fibre 11 in the channel 13, it is fed through the tubular extension 7, and it is then located over the guide block 41 (if this is provided), and then moved downwardly into the groove 47, the chamfer surfaces 49 guiding it into position if it is slightly out of alignment. It will now be in alignment with the channel 13. It is then advanced forwardly into the channel 13, and fed beneath the resilient clamping portion 19, which, because of its inclined orientation relative to the channel 13, has an underface which acts as a chamfer surface to guide and force the leading end of the optical fibre 11 into the channel 13. As this leading end is advanced, it will be forced beneath the curved edge region 31 (the clamping portion 19 can"give"slightly due to the retainer 15 being made of a resilient material such as spring steel). Once in position, the optical fibre 11 will be clamped in position in the channel 13 due to the resilience of the retainer 15. In other words, the resilient clamping portion 19 exerts a downward force on the optical fibre 11 at a contact point 31. In this way, the optical fibre 11 is held against walls 33 of the mounting channel 13.

Referring now to FIGURE 3, there is shown a further embodiment of a retainer 115 in the form of a solid block, for instance made by sintering or moulding. The retainer 115 operates in a similar manner to that shown and described in relation to FIGURE 2 and is again used with the package shown in FIGURE 1. The retainer 115 has two mounting portions or legs 117 that are each

designed to be attached to the substrate upper surface 29 (or the ceramic insulator 21) by a layer of adhesive 35. As in the first embodiment, the retainer 115 "straddles" the mounting channel 13, that is, there is one mounting portion 117 positioned on a part of the substrate upper surface 29 at each side of the longitudinal axis of the channel 13. The retainer 115 has a guiding portion in the form of a chamfer surface 119 bounded by two triangular side walls 120. The chamfer surface 119 terminates in a clamping edge or edge region 131 providing a clamping portion.

The clearance between the clamping portion 131 and the mounting channel 13 is critical so protrusions 123 have been added to the mounting portions 117, the undersides of which rest on the surface 29. The adhesive 35 can then be added to the space adjacent the protrusions 123 to hold the retainer 115 in place.

Alternatively, solder, laser welding or some other attachment method can be used.

The side walls 120 are shown extending parallel to the longitudinal axis of the channel 13. It will be appreciated, however, that they could be inclined inwardly thereto, thus providing chamfer surfaces which assist in guiding the optical fibre into the channel 13. A similar arrangement could be provided on the plate-like retainer 15 shown in FIGURE 2. It is also envisaged that the side walls which define the groove 47 in the guide block 41 could also be chamfered to help guide the optical fibre 11 laterally into the channel 13.

As will be apparent from the earlier description, the guide block 41 which is fitted to, or adjacent, the chip edge 27 provides rough alignment to the channel 13 in the X direction (see FIGURE 3). As the optical component fibre 11 is dropped lower (Y direction) it should feed into the channel 13.

If the fibre 11 is then pushed forward (Z direction) it will strike the chamfer surface 19 ; 119 of the retainer 15 ; 115 and will be forced into the channel 13 and then be clamped in position by the edge 31 ; 131. If the fibre 11 is then pushed forward and lifted at the rear, the edge 31 ; 131 of the retainer 15 ; 115 will act as a fulcrum, holding the front of the optical fibre 11 in the channel 13.

Applying adhesive between the fibre 11, retainer 15 ; 115 and channel 13 will prevent further movement in the Z direction.

It will be understood that the present invention is not limited to the exemplary embodiments which have been described with reference to the accompanying FIGURES but may be varied in many different ways within the scope of the appended claims. For example, the block 119 or the block 45 may be formed of sintered ceramic material.

Claims

CLAIMS :

1. A retainer for retaining an optical component having a generally curvilinear cross section in a mounting channel which extends along the surface of a substrate from a first edge of the substrate, the retainer having a mounting portion and a clamping portion, and including a chamfer surface such that, in use, with the mounting portion attached to the substrate or a support therefor and where the optical component is moved towards the retainer from the first edge of the substrate, the chamfer surface acts to deflect the optical component into the mounting channel and into a position where the optical component is retained in the mounting channel by the clamping portion.

2. A retainer according to claim 1, wherein the chamfer surface deflects the optical component downwardly into the mounting channel.

3. A retainer according to claim 1 or claim 2, wherein the chamfer surface deflects the optical component towards the mounting channel across the surface of the substrate.

4. A retainer according to any one of the preceding claims, wherein the clamping portion comprises a chamfer surface terminating in a clamping edge.

5. A retainer according to any one of claims 1 to 4, wherein the clamping portion comprises a chamfer surface terminating in a clamping edge region.

6. A retainer according to any one of the preceding claims, wherein the clamping portion comprises a resilient portion which is biased such that the resilient portion adopts a first position relative to the mounting portion and wherein, in use, interaction between the resilient portion and the optical component prevents the resilient portion adopting said first position and the resilient portion applies a clamping force on the optical component substantially in the direction of the mounting channel.

7. The retainer according to claim 5, wherein the resilient portion terminates in an arcuate clamping region.

8. The retainer according to any one of the preceding claims, wherein the retainer is formed of spring steel, and the clamping portion is resiliently deformable.

9. The retainer according to any one of claims 1 to 7, wherein the retainer is in the form of a block having a clamping edge.

10. A retainer according to claim 9, wherein the block is formed of a ceramic material.

11. A retainer according to any one of the preceding claims, wherein the chamfer surface, in use, deflects the optical component in a direction normal to the longitudinal axis of the mounting channel.

12. A retainer according to any one of the preceding claims, in combination with a guide block for initially guiding the optical component into the mounting channel, the guide block having a mounting portion and a guiding portion, wherein the guiding portion comprise an upwardly open groove turning at its upper end in two opposed chamfer surfaces, whereby, in use, with the guide block attached or adjacent to the first edge of the substrate with the groove in line with the mounting channel, when the optical component is moved towards the mounting channel, the groove can be used to guide the optical component into line with, and into, the mounting channel.

13. An assembly comprising a substrate having a surface in which is formed a mounting channel which extends from a first edge of the substrate, an optical component having a generally curvilinear cross section disposed in the mounting channel, a retainer having a mounting portion and a clamping portion wherein the mounting portion of the retainer is attached to the substrate or a support therefor such that the clamping portion contacts the optical component to clamp it in the

mounting channel, and optionally a guide block having a mounting portion and a guiding portion wherein the mounting portion is attached to or adjacent the first edge of the substrate, and wherein the retainer includes a chamfer surface for guiding the optical component into the mounting channel.

14. The assembly according to claim 13, wherein the optical component is an optical fibre and the substrate is comprised of an optical chip.

15. The assembly according to claim 13, wherein the optical component is a ball lens and the substrate is comprised of an optical chip.

16. A retainer substantially as hereinbefore described with reference to, and as illustrated in, FIGURES 2 or 3 of the accompanying drawings.

17. An assembly of a retainer, an elongate element of generally curvilinear cross section and a substrate, substantially as hereinbefore described with reference to, and as illustrated in, FIGURES 1 and 2 or FIGURES 1 and 3 of the accompanying drawings.

18. An assembly according to claim 17 and further including a guide block as described with reference to, and illustrated in, FIGURE 2 or FIGURE 3 of the accompanying drawings.

19. A method of guiding an optical component having a generally curvilinear cross section into a mounting channel which extends along the surface of a substrate from a first edge of the substrate comprising the steps of: placing over the mounting channel a retainer having a mounting portion and a clamping portion and a chamfer surface; bringing the optical component in contact with the chamfer surface on the retainer to deflect the optical component into the mounting channel such that the optical component at least partially lies between the mounting channel and the clamping portion of the retainer.

20. A method according to claim 19, further including the step of attaching at, or adjacent, the first edge of the substrate a guide block having a mounting portion and a guiding portion wherein the guiding portion comprises a chamfer surface, the chamfer surface leading to an upwardly opening groove, and using the guide block to line up the optical component with the mounting channel before bringing the optical component in contact with the chamfer surface on the retainer.

21. A method of guiding an optical component having a generally curvilinear cross section into a mounting channel which extends along the surface of a substrate substantially as hereinbefore described with reference to, and as illustrated in, FIGURES 1 and 2 or FIGURES 1 and 3 of the accompanying drawings.